Some nonvolatile storage/memory devices utilize a crystalline state and an amorphous state of a metal compound as storage/memory information and a tellurium compound is typically used as its storage/memory material. The principle thereof is that a difference between a reflectivity of the crystalline state and a reflectivity of the amorphous state of the metal compound is stored as information, which is widely used in optical information storage/memory media such as DVD (Digital Versatile Disk).
In recent years, there has been proposed to use a metal compound for an electric information storage/memory medium. The method of using a metal compound for an electric information storage/memory medium is, unlike the optical method described above in which a metal compound is used for an optical information storage/memory medium, an electric method of detecting a difference in an electric resistance between the crystalline state and the amorphous state of the metal compound, that is a difference between a low resistance state of crystal and a high resistance state of amorphia on the basis of the amount of current or a change in voltage. For example, U.S. Pat. No. 6,750,469 (Patent Document 1) discloses an electric information memory medium using a metal compound called phase-change memory or phase-change type memory.
A structure of a basic memory cell of the phase-change memory is configured such that a memory element (phase-change material) and a selection element are combined. The phase-change memory stores and holds information by making the memory element into the crystalline state or the amorphous state by Joule heat generated in the memory element by applying a current from the selection element. The rewriting can be performed such that, in the case of obtaining the amorphous state with an electrically high resistance, a high current is applied to set a temperature of the memory element to be higher than a melting point and then rapidly cooling down the memory element. In the case of obtaining the crystalline state with an electrically low resistance, the current to be applied is restricted to set the temperature of the memory element to be a crystallization temperature lower than the melting point. Generally, the resistance value of the memory element is changed by 2 digits or 3 digits according to the phase change. Thus, the phase-change memory has a read signal to be largely different depending on whether the memory element is in the crystalline state or the amorphous state and is thus easy to perform a sensing operation.
For example, U.S. Pat. No. 6,579,760 (Patent Document 2) discloses a phase-change memory having cross-point memory cells which can be manufactured at a low cost.